Explore Edinburgh in Google Street View

Edinburgh is two cities that were built to different rules and left side by side, and Street View makes the join obvious in a way a photograph never does. The Old Town runs along a ridge of volcanic rock with the castle at the high end, and because the ridge is narrow the medieval city grew upward and sideways into closes rather than outward into streets. The New Town, a few hundred metres north across what used to be a loch, is a Georgian grid laid out in 1767 with straight lines and matching frontages.

Walk the Royal Mile from the castle down to Holyrood and you are on the spine of the old city. What is worth doing while you are on it is looking sideways. Every few metres a gap in the frontage leads into a close, a narrow passage running steeply down off the ridge, and a surprising number of them were photographed on foot. They are the oldest surviving fabric in the city and they are invisible from the main street.

The vertical layering is the thing people find hardest to believe until they see it. Because the ground falls away steeply on both sides of the ridge, a building's front door on the Royal Mile can be four storeys above its back door. Bridges here cross other streets rather than water: stand on George IV Bridge and look over the parapet and there is a road below you with its own shopfronts.

Victoria Street is the single most photographed curve in Scotland and it earns it. A shallow arc of coloured shopfronts with a terrace above them, it was cut in the 1830s to link the Royal Mile down to the Grassmarket, and the terrace exists because the engineers had to do something with the level difference. It is worth opening at both levels, because the view from the terrace and the view from the road are two different streets.

The New Town is the opposite experience and should be taken slowly. Charlotte Square and Moray Place are the set pieces, but the reward is in the lanes behind the main terraces, the mews that were built for horses and are now houses. Circus Lane is the one people photograph, a cobbled curve of low buildings with a church spire lined up at the end of it, and the imagery is good because the lane is quiet enough to walk.

For something that is not a street at all, Arthur's Seat sits inside the city: an extinct volcano with footpaths over it, several of which were captured on foot. From the top you are looking down on the whole ridge, the New Town grid and the Firth of Forth behind it, which is the clearest way to understand how the place is put together before going back down into it.